The present invention relates to an exhaust re-combustion type (combustion stabilizing type) combined cycle power generation plant, which combines a gas turbine plant and a steam turbine plant arranged independently from each other in their axes.
Nowadays, a combined cycle power generation plant operated as a practical plant includes an exhaust re-combustion type in addition to an exhaust heat recovery type. The exhaust re-combustion type combined cycle power generation plant is constructed in a manner that a gas turbine plant and a steam turbine plant are arranged in their axes independently from each other but operatively connected to each other, which includes a case where both the gas turbine plant and the steam turbine plant are newly founded and also includes a case of combining the existing steam turbine plant with a newly founded gas turbine plant, so-called re-powering system used as a feed water heating cycle. The exhaust re-combustion type combined cycle power generation plant incorporating such re-powering system is excellent in the following points. That is, such plant has a simple system, makes great a power factor of the steam turbine and is adaptable to a power increase of the existing power generation plant. Thus, this plant is applicable to some thermal power generation plants.
FIG. 4 shows a configuration of a conventional power plant.
Referring to FIG. 4, a reference numeral 1 denotes the whole configuration of a conventional exhaust re-combustion type combined cycle power generation plant including a gas turbine plant 2, a boiler 3 and a re-heat type steam turbine plant 4.
The gas turbine plant 2 includes a power generator 5, an air compressor 6, a gas turbine combustor 7 and a gas turbine B. An air sucked by the air compressor 6 is compressed therein to a high pressure, and then, the high pressure air (pressurized air) is guided to the gas turbine combustor 7. Further, a fuel is added in the gas turbine combustor 7 to the high pressure air to generate a combustion gas, which is then expanded by the gas turbine 8 so that the power generator 5 can be driven by a rotating torque generated by the expansion of the combustion gas.
The gas turbine plant 2 guides the combustion gas expanded by the gas turbine 8 to the boiler 3 as an exhaust gas G to heat the exhaust gas G by the combustion gas of the boiler 3.
On the other hand, the re-heat type steam turbine plant 4 includes a steam turbine section 9 and a condensate and feed water system 10.
The steam turbine section 9 is constructed in a manner that a high pressure turbine 11, an intermediate pressure turbine 12, a low pressure turbine 13 and a power generator 14 are mutually connected directly in their axes. That is, the driving shafts or rotating shafts thereof are operatively connected. A main steam MS supplied from the boiler 3 is expanded by the high pressure turbine 11, and then, the turbine exhaust gas is heated by a reheater 15, and further, is guided into the intermediate pressure turbine 12 as a reheated steam RS. After being expanded, the turbine exhaust gas is again expanded by the low pressure turbine 13 so that the power generator 14 can be driven by a rotating torque generated accompanying with the expansion of the turbine exhaust gas.
The condensate and feed water system 10 includes a condenser 16, a low pressure feed water heater 17, a deaerator 18, a high pressure feed water heater 19, a low pressure gas cooler 20 arranged in parallel with the low pressure feed water heater 17, and a high pressure gas cooler 21 arranged in parallel with the high pressure feed water heater 19. The turbine exhaust gas from the low pressure turbine 13 is condensed into a condensate water CW by the condenser 16, and then, the condensate water CW makes a heat-exchange with a turbine extraction steam ES from the low pressure turbine 13 by the low pressure feed water heater 17 so as to be reproduced into a feed water FW. Further, the feed water FW is mixed with the turbine extraction steam ES from the low pressure turbine 13 so as to be heated and deaerated by the deaerator 18, and then, the feed water FW after heated and deaerated makes a heat-exchange with a turbine extraction steam ES from the intermediate pressure turbine 12 by the high pressure feed water heater 19 so as to be re-produced into a higher temperature feed water, and thereafter, is returned to the boiler 3.
On the other hand, in the boiler 3, the exhaust gas G supplied from the gas turbine plant 2 is heated by a boiler combustion gas, and then, the heated gas HG makes a heat-exchange with the feed water FW by the high pressure gas cooler 21, and thereafter, again makes a heat-exchange with the feed water FW by the low pressure gas cooler 20 so that the feed water can be reproduced into a higher temperature feed water.
In the manner described above, in the exhaust re-combustion type combined cycle power generation plant 1 incorporating the re-powering system of the structure mentioned above, the exhaust gas discharged from the gas turbine plant 2 is heated by the boiler 3, and then, the heated gas HG is used as a heat source to heat the feed water FW. Thus, a heat recovery can be effectively achieved, and a heat efficiency of the plant can be improved.
In the recent gas turbine plant 2, in order to achieve a higher heat efficiency and high power generation, there has been made a plan to heighten a combustion gas temperature (gas turbine inlet temperature) from usual 1100.degree. C. to 1300.degree. C. or 1500.degree. C. or more.
In the gas turbine plant 2, conventionally, in order to cope with high temperature of the gas turbine, a cooling air is supplied to components of the gas turbine 8, for example, a gas turbine stationary blade, a gas turbine rotating blade, a gas turbine rotor, etc., and thus, maintenance of their component strength has been achieved. Further, a part of high pressure air generated by the air compressor 6 is utilized as the cooling air.
However, the high pressure air generated by the air compressor 6 is originally used for driving the gas turbine 8, and in the case where the part of the high pressure air generated by the air compressor 6 is used for cooling these components of the gas turbine 8, there has arisen a problem that a desired plant heat efficiency is not obtained. Further, the high pressure air generated by the air compressor 6 cools the components of the gas turbine 8, and thereafter, is joined together with a main flow (gas turbine driving gas). For this reason, the high pressure air give disturbance to the main flow, and as a result, there has arisen a problem that a blade efficiency is lowered and a desired power output is not obtained. Thus, with progress of the plan to make high temperature the gas turbine plant 2, the use of the high pressure air as a coolant for components of the gas turbine 8 has no longer given a limit in the high plant heat efficiency. Recently, a study and development of a cooling medium for components of the gas turbine 8 have been newly made, and there is a plan to use a steam having a specific heat higher than air as the cooling medium.
In the case of using a steam as the cooling medium, in the exhaust re-combustion type combined cycle power generation plant incorporating the re-powering system, from the relation of cooling the steam after making it into a proper temperature between the main flow (gas turbine driving gas) and the components of the gas turbine 8, a turbine exhaust gas (steam before being supplied to the reheater 15) of the high pressure turbine 11 is selected as the cooling medium supply source. Considering that the temperature of the main flow is more than 1300.degree. C., the steam thus selected serves to preferably cool the components of the gas turbine 8 without generating an excessive thermal stress in the components of the gas turbine 8.
However, the steam after cooling the components of the gas turbine 8 has inconvenience and disadvantage in a plant operation if the selection of a place for recovering the steam is erroneously made. More specifically, the cooling steam flows in a serpentine shape when cooling the components of the gas turbine 8, and for this reason, a pressure loss becomes extremely large. Thus, in the exhaust re-combustion type combined cycle power generation plant 1, in order to cover a short of pressure of the turbine exhaust gas used as a cooling steam, a main steam MS supplied to the high pressure turbine 11 from the boiler 3 must be further made high pressure. This causes a disadvantage in an efficiency of the boiler. Further, a temperature of the steam which has cooled the components of the gas turbine 8 rises when cooling, and then, becomes about 550.degree. C. The steam temperature becomes lower as compared with a reheated steam RS discharged from the reheater 15 because the reheated steam has a temperature of 600.degree. C. If the low temperature steam is joined together with the reheated steam RS, the temperature of the reheated steam RS becomes further low, thus being not preferable in a steam turbine efficiency.